The film tells a story of the relationship between a woman, Summer (Deschanel), who doesn't believe in true love and a man, Tom (Gordon-Levitt), described as a hopeless romantic, who falls in love with her. When Tom is blindsided after his girlfriend Summer dumps him, he shifts back and forth through various periods of their 500 days 'together' to try to figure out where things went wrong. His reflections ultimately lead him to finally rediscover his true passions in life.